Television display apparatus provided with a circuit arrangement for generating a sawtooth current through a line deflection coil

ABSTRACT

Television display apparatus including a circuit arrangement for combined line deflection and supply voltage stabilisation with the aid of means for field frequency modulation of the line deflection current, and a circuit arrangement for use in such television display apparatus.

United States Patent 1 1 Verbeij [4 1 Oct. 21, 1975 TELEVISION DISPLAYAPPARATUS PROVIDED WITH A CIRCUIT ARRANGEMENT FOR GENERATING A SAWTOOTHCURRENT THROUGH A LINE DEFLECTION COIL Inventor: Oswald JohannesVerbeij,

Eindhaven, Netherlands Assignee: U.S. Philips Corporation, New

York, N.Y.

Filed: Dec. 4, 1973 Appl. No.: 421,5 14

Foreign Application Priority Data Jan. 2, 1973 Netherlands 7300001 US.Cl 315/371; 315/379 Int. Cl. I-IOIJ 29/56 Field of Search 315/27 R, 27TD, 276 D,

[56] References Cited UNITED STATES PATENTS 3,689,797 9/1972Hetterscheid et al 315/276 D 3,691,422 9/1972 Boekhorst 315/276 D3,748,531 7/1973 Bockhorst et al 315/276 D 3,803,447 4/1974 Wolber315/27 SR Primary Examiner.Maynard R. Wilbur Assistant Examiner-.l. M.Potenza Attorney, Agent, or Firm-Frank R. Trifari; Henry I. Steckler[57] ABSTRACT Television display apparatus including a circuitarrangement for combined line deflection and supply voltagestabilisation with the aid of means for field frequency modulation ofthe line deflection current, and a circuit arrangement for use in suchtelevision display apparatus.

10 Claims, 10 Drawing Figures US. Patent Oct. 21, 1975 Sheet 1 of 53,914,650

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US. Patent Oct. 21, 1975 Sheet 2 of5 3,914,650

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US. Patent 0m. 21, 1975 Sheet4 of5 3,914,650

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U.S. Patent Oct. 21, 1975 Sheet 5 of5 3,914,650

TELEVISION DISPLAY APPARATUS PROVIDED WITH A CIRCUIT ARRANGEMENT FORGENERATING A SAWTOOTH CURRENT THROUGH A LINE DEFLECTION COIL Theinvention relates to television display apparatus provided with acircuit arrangement for generating a sawtooth current through a linedeflection coil forming part of a resonant network also including atrace capacitor and a retrace capacitor, switching means for applyingthe voltage across the trace capacitor to the deflection coil at theline frequency during the trace time of the sawtooth current, saidswitching means being blocked during the retrace time, a first currentloop comprising a winding of an inductive element and a controllableswitch for supplying energy originating from a direct voltage source tothe inductive element during the conduction period of the switch and asecond current loop comprising a diode and a winding of said inductiveelement which is connected through the diode to the resonant network,and a field deflection current generator.

Such a circuit arrangement is described in the publication IEEETransactions on Broadcast and Television Receivers, August 1972, volumeBTR-IS, No. 3, pages 177 to 182, and is the combination of a linedeflection circuit and a switched supply voltage stabilising circuit inwhich a single controlled switch serves for fulfilling the two saidfunctions. The circuit arrangement has the advantage that it can be fedwith an unstabilised supply voltage and can supply a satisfactorilystabilised sawtooth current and a stabilised high voltage and possibleauxiliary voltages. In the known circuit arrangement this stabilisationis obtained by applying the voltage across the trace capacitor as acontrol voltage to a driver circuit which supplies the switching pulsesfor the controllable switch (for example, a transistor) and whichcontrols the conduction period of the switch under the influence of thiscontrol voltage.

Due to this stabilisation the known circuit arrangement cannot be usedwithout any difficulty in arrangements, for example, colour televisiondisplay apparatus in which the line deflection must undergo a so-calledeast-west modulation for correcting the raster distortion. It ispossible to control the driver circuit with a field frequency varyingsignal in such a manner that the deflection current is modulated butthis also results in an unwanted modulation of the high voltage andother auxiliary voltages generated with the aid of the circuitarrangement. The above-mentioned publication states that a possiblesolution is formed by the combination with a known modulator or with aseparate EHT generator. As is known, in the first case the modulator andthe circuit arrangement must form part of a bridge circuit and in thesecond case the said generator must be decoupled relative to the circuitarrangement. Alternatively, an EHT generator which is completelyseparated from the circuit arrangement can be used.

The said solutions lead to more or less complicated and hence costlycombinations. It is an object of the present invention to provide acircuit arrangement which is very simple in which east-west modulationof the deflection current is possible without the high voltage andauxiliary supply voltages derived therefrom undergoing this modulation,while both the deflection current and the high voltage and the auxiliarysupply voltages are stabilised against fluctuations of the supplyvoltage which is generally derived from the electric mains. The circuitarrangement according to the invention maintains the important advantageof the known arrangement, viz. that both the line deflection and thesupply voltage stabilisation include one and the same switch. To realizethe abovementioned advantages the circuit arrangement according to theinvention is characterized in that a modulation source controlled by thefield deflection current generator is incorporated in the second currentloop for modulating the amplitude of the sawtooth current, the circuitarrangement furthermore including a stabilising circuit for maintainingthe amplitude of thevoltage occurring across the inductive elementduring the retrace time of the sawtooth current substantially constantby varying the conduction period of the switch.

In order to maintain the energy dissipated in the modulation source orto be supplied by this source sufficiently low and also to prevent thefield frequency east-west modulation from covering a too large part ofthe admitted variation range of the conduction period of thecontrollable switch, the television display apparatus according to theinvention is preferably furthermore characterized in that the saidmodulation source provides a line frequency voltage with line flybackpulses which are varied in amplitude in accordance with the fieldfrequency.

The invention will further be described with reference to the Figuresshown in the drawing.

FIG. 1 shows a first embodiment of a television display apparatusaccording to the invention,

FIG. 2 shows some voltage and current curves to explain the operation ofthe embodiment of FIG. 1 and FIGS. 3 to 10 show other embodiments ofcircuit arrangements in a television display apparatus according to theinvention.

The television display apparatus of FIG. 1 includes an RF tuner 1 forconnection to an aerial 2, an IF amplifier 3, a detector 4 and a videoamplifier with a color decoder 5 applying the, color signals to a colordisplay tube 6. This tube has a final anode 7 and is provided with acoil L for the horizontal (line frequency) deflection and with a coil Ufor the vertical (field frequency) deflection.

Line synchronizing pulses which are applied to a line oscillator 9 andfield synchronizing pulses applied to a field oscillator 10vareseparated with the aid of a sync separator 8 from the output signalfrom detector 4. Oscillator 10 controls a field output stage 1 lsupplying the deflection current for the coil L Line oscillator 9controls a driver stage D, supplying switching pulses for a switchingtransistor T, of a line deflection output circuit to be furtherdescribed.

A trace capacitor C is arranged in series with line deflection coil Lyand a diode D having the given conductivity direction and a retracecapacitor C are connected in parallel with the series arrangement thusformed. The retrace capacitor C may alternatively be arranged inparallel across coil Ly. The said four elements only show the principlecircuit diagram with the main components of the deflection section. Thissection may be provided, for example, in known manner with one or moretransformers for mutual coupling of the elements, with circuits forcentering and linearity correction and the like.

A secondary winding L of a transformer A is in series with a diode Dwhose cathode is connected to the junction of elements D,, C and Ly andto the anode of a diode D The cathode of diode D is connected to one endof a primary winding L, of transformer 'A and to the collector oftransistor T, which is of the npn type. The positive terminal of adirect voltage source B is connected to the other end of winding L, andthe negative terminal is connected to ground. The free ends of elementsD,, C C, and the emitter electrode of transistor T, are also connectedto ground.

A further winding L is wound on the core of transformer A one end ofwhich is connected to ground while the other end is connected to theanode of a rectifier D whose cathode is connected to earth through acapacitor C The output voltage of rectifier D is applied to drivercircuit D, for controlling the conduction period of the transistor T,.Windings L, and L preferably have the same number of turns. The windingsense of the transformer windings is denoted by polarity dots in theFigure.

A modulation source M is included between the end of Winding L remotefrom diode D and ground. This modulation source includes an emitterfollower transistor T, arranged between said end of winding L and groundand a capacitor C connected in parallel across its emittercollector pathas well as a driver stage D, controlling the base electrode oftransistor T, which stage is connected to the field output stage 11.Driver stage D, generates a field frequency parabolically varyingmodulation voltage V,,, from the signals of the field output stage andthis voltage is also active through emitter follower T, at the low sideof winding L Modulation voltage v serves for the east-west rastercorrection of the line deflection current. Voltage v varies inaccordance with the field frequency but may be considered as a constantvoltage during a line period. Since the raster distortion to becorrected is generally pin-cushion shaped, it is known that theintroduced modulation must be such that the amplitude of the linedeflection current varies with a parabolic envelope with the peak of theparabola occurring in the middle of the field scan time and coincidingwith the maximum amplitude.

Further windings are wound on the core of transformer A across whichthere are voltages which serve as supply voltages for other parts of thetelevision display apparatus. One of these windings, winding L is shownin FIG. 1 and generates the EHT for the final anode 7 of televisiondisplay tube 6 with the aid of an EHT rectifier D across a smoothingcapacitance C The supply voltages thus obtained as well as the EHT mustnot undergo the same field frequency modulation as the line deflectioncurrent. In addition, like this current, they must be stabilised againstfluctuations of the voltage V of source B generally derived from theelectric mains. Both requirements are satisfied in accordance with theinvention because the voltage across capacitor C, which is obtained bypeak rectification of the flyback pulses present across winding L isapplied to driver circuit D,. Driver D, includes a comparison stage anda modulator which ensure in known manner that the conduction period oftransistor T, is varied.

The operation of the circuit arrangement of FIG. 1 will be explainedwith reference to the curves of FIG. 2. In FIG. 2a the voltage v, acrosscapacitor C in FIG. 2b the voltage v across winding L and in FIG. thecurrent i, through winding L, and the current i through winding L areplotted as a function of time with T denoting the line period. Theretrace time is denoted by t, while (1 8) t, denotes the part of thetrace time t, during which transistor T, is cut off and 8 t, denotes thepart where transistor T, conducts. As will be apparent the number 8 isto be between 0.5 and 1.

After the commencement t of the trace diode D, conducts. The voltageacross capacitor C, is applied to deflection coil Ly so that a sawtoothdeflection current flows through this coil. When the deflection currentreverses its direction approximately in the middle of trace t,, diode D,is blocked but in this case the deflection current flows through diode Dand the then conducting transistor T,. Since the polarity of thedeflection current is reversed approximately in the middle of trace t,and since it must be possible for the deflection current to flowunhampered through transistor T,. during the second half of the trace,it will be evident that the instant t, when the transistor is renderedconducting is to be before the middle of the trace. This means that 8must be more than 0.5.

At the end t of the trace transistor T, is cut off. A sinusoidal flybackvoltage is produced across capacitor C At an instant t the voltage vbecomes zero again so that diode D, is rendered conducting: this is thecommencement of a new trace.

During the part 8 t, of the trace when transistor T, is conducting, alinearly increasing current i, flows through winding L,. Thus current i,flows through transistor T, as well as the deflection current whichflows via diode D after the deflection current has reversed itsdirection. When at the instant t transistor T, is cut off not only thecurrent path for the deflection current but also that for current i, isinterrupted. The latter results in a current i, flowing in secondarywinding l whose initial value (in case of equal numbers of turns betweenL, and L is equal to the final value of i,. The current i, renders diodeD conducting against the flyback pulse v then occurring at the cathodeof diode D,,. As a result the flyback pulse appears on the high side ofwinding L and magnetically also on the low side of winding L,, at thecollector of transistor T, and at the cathode of diode D which isblocked thereby.

Also after the instant t when the retrace ends diode D remainsconducting until transistor T, is rendered conducting; current i becomeszero and current 1', starts to flow.

When V, is the direct voltage across capacitor C, if this has asufficiently large capacitance or when it is the direct voltagecomponent of the voltage across capacitor C, if this has a relativelylow capacitance for the S correction, then V is equal to the mean valueof v,. In fact no direct voltage component can be present across coilLy. There applies:

l I V, T I v dr Voltage v is equal to the difference between the voltageat the anode of diode D and modulation voltage V During the intervalbetween t and t, the former voltage is zero (diodes D and D, conduct) sothat v v so that the current i,, is sawtooth-shaped while with L theinductance of the transformer on windings L and L During retrace t, theanode voltage of diode D is equal to voltage v because diode D conductsso that v, v v while current i; is given by During the interval betweent, and t the collector voltage of transistor T, is zero so that voltageV prevails across winding L, and hence across winding L This voltage maybe considered constant during a line period. In this interval thesawtooth current i, flows through the winding L in which L di The meanvalue of voltage v i.e. the voltage across an inductor, must be zero.The surface in FIG. 2 shaded to the right must thus be equal to thesurface shaded to .the left so that there applies:

v (l 8) n+v 8 r, z v dtv t v v o In this formula V, can be filled in:

m v, a r, v (T a 1,)

in such a manner that the amplitude of the voltage across the winding Land hence the amplitude v,,-

I v v of voltage v always remains constant. Since voltage v dependent onthe ratio is proportional to the amplitude v of voltage v it followsfrom the foregoing that voltage V,, and hence the amplitude ofthedeflection current varies with the variation of voltagev which isdesirable. On the other hand variations of supply voltage V, do not haveany influence on voltage V,,. Formula (I) shows that the variation ofthe number 8 accounts for both that of voltage V and that of v Theamplitude v always remains constant independent of the variations in thevoltages V and v The same applies to the amplitudes of the voltagesacross windingL, and across the other windings (not shown) oftransformer A. The EHT and the auxiliary supply voltages obtained in acorresponding manner are therefore not east-west modulated and areindependent of the fluctuations in the main supply voltage V In apractical example supply voltage V varies between approximately 240 and340 V while the desired variation of voltage V, ranges fromapproximately 138 to 148 V. In case of a ratio z 0.15 formula (I)becomes:

V V (V v 8 (l-z) (V v 0.85 6

(Z) and The mean value of voltages V and V, are 290 V and 143 V,respectively. When the control of driver D, is adjusted by the voltageacross C in such a manner that the number 8 is in the middle of itsvariation-range, i.e. 8 0.75, there follows from formula (2) that themean value of v l 18 V and from formula (3):

v =1 O V v 1548 V.

- The other values of v and 8 can be calculated with the aid of formulas(2) and (4). At the extreme values of V and v we find:

Since the number 6 remains within the admissible limits, i.e. 0.5 and 1it is found that the circuit arrangement of FIG. 1 can be realized forthe given variations of voltages V and V,,. It is also found thatvoltage v must always be negative so that the straight piece of the linebetween the instants t and t in FIG. 2b is located above the time axiswhile current i, in FIG. 20 will linearly decrease between the sameinstants.

In practice source M may be formed as a passive element. In fact, thecurrent i flowing through this element produces a negative voltage dropthereacross. Such an element may be a field frequency varying resistor,for example, formed as a controlled transistor. However, since current idepends on the number 8 and hence on voltage V source M must have a lowinternal resistance so that voltage v cannot be influenced by voltage VSuch a source is, for example, the transistor- T, arranged as an emitterfollower which re- -ceives a field frequency parabola signal through thecontrol circuit D, in such a manner that the voltage at the junction ofwinding L and transistor T, is always negative relative to the earthpotential and that the peak of the parabola in the middle of the fieldscan time is less negative than the values at the commencement and atthe end of this time. A capacitor .C bypasses the said junction for linefrequency signals.

It will be ,evident that in the arrangement of FIG. 1 diode D may bereplaced in known manner by the parallel arrangement of a transistor anda diode, in which the transistor mustbe line-frequency controlled, forexample, by driver circuit D, and in which diode D can be omitted. It isobvious that the operation remains the same. This also applies to theembodiments which will now be described.

Possible modifications of the known circuit arrangement are described inNetherlands Pat. application No. 7217254 (PHN 6677). Similarmodifications are also possible with those of FIG. 1. In FIGS. 3 and 4two of these modifications are shown in which the same referencenumerals have been used for the same elements as in FIG. 1 and in whichwindings L and L are replaced by one winding L. As described in the saidNetherlands patent application these modifications have the advantagethat a leakage inductance of the transformer A cannot have a detrimentalinfluence. In FIG. 4 a capacitor C operates as a supply voltage sourcewhose charge is replented through a choke L from direct voltage sourceB.

FIG. 5 shows an embodiment of the circuit arrangement according to theinvention which has a similar operation as that of FIG. 1 with thedifference that voltage v between instants t and is not equal to -V butto V v Similar formulas as those above may be derived explaining thevariation of the number 8 in case of variation of voltages v and v FIGS.6 and 7 show modifications of the embodiment according to FIG. 5 whichmodifications are derived in the same manner from FIG. 5 as those ofFIG. 3 and FIG. 4 are derived from FIG. 1.

It is to be noted that in all modifications modulation source M formspart of a current loop which comprises windings L and L and diode D andwhich is closed through the deflection section D C L C In themodifications of FIGS. 4, 5, 6 and 7 modulation source M also forms partof the current loop comprising windings L and L and transistor T andwhich is closed through direct voltage source B and the capacitor Coperating as a direct voltage source, respectively.

Since only the amplitude of the voltage across winding L is maintainedconstant during the line flyback time it is only sufficient, accordingto a further aspect of the invention, to choose a field frequencyvarying voltage for the voltage V which voltage occurs only during thesaid line retrace. Even a part thereof, namely just before and after themiddle of the line retrace is sufficient. When in addition voltage v iszero in the interval between t and t the power dissipated or supplied bythe modulation source is also zero during this interval. The value ofvoltage v in the interval between t, and 1 is less important becausediode D is then blocked. A further advantage is that the variation ofthe number 8 caused by the east-west modulation is slighter which hashas been proved in practice.

An embodiment of this principle is shown in FIG. 8. The modulationsource now includes an extra transformer winding L which appliesnegatively directed flyback pulses through the control circuit D, to theemitter follower transistor T,. In control circuit D, the attenuation oramplification of the flyback pulses is field frequency parabolicallyvaried by means of the control from field output stage 11. Themodulation voltage v on the low side of winding L thus consists of fieldfrequency amplitude varying line flyback pulses causing the east-westmodulation of the line deflection current. The positive voltage on thelow side of winding L during the time between t and 2 has no influenceon the modulation voltage because then transistor T, is saturated.During the entire line scan time modulation voltage v is therefore equalto zero so that transistor T, does not dissipate energy during thistime. It can be proved that in this embodiment the conduction period (8)of the transistor T,- is only variedby supply voltage (V variations andnot by variations of the modulation voltage v Instead of being derivedfrom a transformer winding the flyback pulses for the control circuit D,may alternatively be derived from the retrace capacitor C FIG. 9 showsanother embodiment based on the same principle. The modulation source Mof FIG. 4 is consti tuted in FIG. 9 by a coil L whose inductance varieswith the field frequency and parabolically. Such a coil is known and maybe formed as a power winding of a saturable reactor whose controlwinding receives a field frequency current. A voltage is present acrosscoil L; which voltage is a field frequency varying fraction of thevoltage across the series arrangement of L and L. The latter voltage isequal to voltage v during the retrace and in the interval between t andr this voltage is equal to zero and in the interval between 1 and it isequal to the voltage V of capacitor C The energy applied by inductor Lto the deflection section through D during the retrace is repleted againfrom capacitor C during the interval between t, and t In the modulationmethod of FIG. 9 modulation source L thus dissipates nothing except forthe energy required for the control of this source.

Another embodiment is shown in FIG. 10. Diode D I is displaced to thelow side of winding L and an additional transformer winding L, withconsiderably fewer turns than winding L is arranged between diode D andmodulation source M. The cathode of a further diode D is connected tothe cathode of diode D and its anode is connected to earth. Modulationsource M supplies a negative parabola field frequency varying directvoltage so that only the peaks of the flyback pulses across winding Lcause diode D to conduct. Modulation source M thus is only active duringthese peaks in the current loop L D L and the deflection section D C Ly,C and only during these peaks does source M supply or dissipate energy.During the other part of the retrace and during the interval between tand t of the trace diode D is conducting and takes over the normalfunction of D of FIG. 1. Diodes D and D are both blocked during theconducting period between t and 1 of transistor T What is claimed is:

1. Television display apparatus provided with a circuit arrangement forgenerating a sawtooth current through a line deflection coil formingpart of a resonant network also including a trace capacitor and aretrace capacitor, switching means for applying the voltage across thetrace capacitor to the deflection coil at the line frequency during thetrace time of the sawtooth current, said switching means being blockedduring the retrace time, a first current loop comprising a winding of aninductive element and a controllable switch for supplying energyoriginating from a direct voltage source to the inductive element duringthe conduction period of the switch and a second current loop comprisinga diode and a windingof said inductive element which is connectedthrough the diode to the resonant network and a field deflection currentgenerator, characterized in that a modulation source controlled by thefield deflection current generator is incorporated in the second currentloop for modulating the amplitude of the sawtooth current, the circuitarrangement furthermore including a stabilizing circuit for maintainingthe amplitude of the voltage occurring across the inductive elementduring the retrace time of the sawtooth current substantially constantby varying the conduction period of the switch.

2. Television display apparatus as claimed in claim 1, characterized inthat the modulation source includes an emitter follower stageincorporated in said second current loop as well as a control device forfield frequency controlling the emitter follower stage.

3. Television display apparatus as claimed in claim 1, characterized inthat the modulation source supplies a line frequency voltage with lineflyback pulses with a field frequency amplitude variation.

4. Television display apparatus as claimed in claim 3, characterized inthat the modulation source supplies a line frequency voltage which issubstantially zero at least during the part of the line trace time whenthe controllable switch is blocked.

' SQ-Television display apparatus as claimed in claim 2 andcharacterized in that the modulation source supplies a line frequencyvoltage with line flyback pulses with a field frequency amplitudevariation and line flyback pulses originating from a winding of theinductive element control the emitter follower stage through a fieldfrequency amplification-controlled control circuit.

6. Television display apparatus as claimed in claim 3, characterized inthat the modulation source is constituted by a controllable inductor,for example, the power winding of a saturable reactor.

7. Television display apparatus as claimed in claim 1, characterized bythe series arrangement of the modulation source with a winding on theinductive element and with the third diode in which a further diode ispresent in parallel across the said series arrangement.

8. Television display apparatus as claimed in claim 1, characterized inthat the modulation source is incorporated both in the first and in thesecond current loop.

9. Television display apparatus as claimed in claim 1, characterized inthat the switching means consist of a parallel diode and the seriesarrangement of a series diode and the controllable switch connected inparallel therewith.

10. A circuit arrangement for generating a sawtooth current through aline deflection coil, said circuit arrangement comprising a tracecapacitor and a retrace capacitor forming a resonant circuit with saidcoil; switching means for applying the voltage across the tracecapacitor to the deflection coil at the line frequency during the tracetime of the sawtooth current, said switching means being blocked duringthe retrace time; a first current loop comprising a winding of aninductive element and a controllable switch means coupled to saidelement for supplying energy originating from a direct voltage source tothe inductive element during the conduction period of the switch; asecond current loop comprising, a field deflection current generator, adiode, a winding of said inductive element coupled through the diode tothe resonant network and to said field deflection current generator, anda modulation source means controlled by the field deflection currentgenerator .for modulating the amplitude of the sawtooth current; and astabilizing circuit means for maintaining .the amplitude of the voltageoccurring across the inductive element during the retrace time of thesawtooth current substantially constant by varying the conduction periodof the switch.

1. Television display apparatus provided with a circuit arrangement forgenerating a sawtooth current through a line deflection coil formingpart of a resonant network also including a trace capacitor and aretrace capacitor, switching means for applying the voltage across thetrace capacitor to the deflection coil at the line frequency during thetrace time of the sawtooth current, said switching means being blockedduring the retrace time, a first current loop comprising a winding of aninductive element and a controllable switch for supplying energyoriginating from a direct voltage source to the inductive element duringthe conduction period of the switch and a second current loop comprisinga diode and a winding of said inductive element which is connectedthrough the diode to the resonant network and a field deflection currentgenerator, characterized in that a modulation source controlled by thefield deflection current generator is incorporated in the second currentloop for modulating the amplitude of the sawtooth current, the circuitarrangement furthermore including a stabilizing circuit for maintainingthe amplitude of the voltage occurring across the inductive elementduring the retrace time of the sawtooth current substantially constantby varying the conduction period of the switch.
 2. Television displayapparatus as claimed in claim 1, characterized in that the modulationsource includes an emitter follower stage incorporated in said secondcurrent loop as well as a control device for field frequency controllingthe emitter follower stage.
 3. Television display apparatus as claimedin claim 1, characterized in that the modulation source supplies a linefrequency voltage with line flyback pulses with a field frequencyamplitude variation.
 4. Television display apparatus as claimed in claim3, characterized in that the modulation source supplies a line frequencyvoltage which is substantially zero at least during the part of the linetrace time when the controllable switch is blocked.
 5. Televisiondisplay apparatus as claimed in claim 2 and characterized in that themodulation sourcE supplies a line frequency voltage with line flybackpulses with a field frequency amplitude variation and line flybackpulses originating from a winding of the inductive element control theemitter follower stage through a field frequencyamplification-controlled control circuit.
 6. Television displayapparatus as claimed in claim 3, characterized in that the modulationsource is constituted by a controllable inductor, for example, the powerwinding of a saturable reactor.
 7. Television display apparatus asclaimed in claim 1, characterized by the series arrangement of themodulation source with a winding on the inductive element and with thethird diode in which a further diode is present in parallel across thesaid series arrangement.
 8. Television display apparatus as claimed inclaim 1, characterized in that the modulation source is incorporatedboth in the first and in the second current loop.
 9. Television displayapparatus as claimed in claim 1, characterized in that the switchingmeans consist of a parallel diode and the series arrangement of a seriesdiode and the controllable switch connected in parallel therewith.
 10. Acircuit arrangement for generating a sawtooth current through a linedeflection coil, said circuit arrangement comprising a trace capacitorand a retrace capacitor forming a resonant circuit with said coil;switching means for applying the voltage across the trace capacitor tothe deflection coil at the line frequency during the trace time of thesawtooth current, said switching means being blocked during the retracetime; a first current loop comprising a winding of an inductive elementand a controllable switch means coupled to said element for supplyingenergy originating from a direct voltage source to the inductive elementduring the conduction period of the switch; a second current loopcomprising, a field deflection current generator, a diode, a winding ofsaid inductive element coupled through the diode to the resonant networkand to said field deflection current generator, and a modulation sourcemeans controlled by the field deflection current generator formodulating the amplitude of the sawtooth current; and a stabilizingcircuit means for maintaining the amplitude of the voltage occurringacross the inductive element during the retrace time of the sawtoothcurrent substantially constant by varying the conduction period of theswitch.